a. Field of the Invention
This invention relates to electrical safety switches.
b. Related Art
Environments requiring the switching of electrical circuits will often call for the use of a safety switch. For example, safety switches are commonly used to control the power input to machinery or as the power switch to one or more areas of the physical plant.
An example of a conventional spring operated electrical safety switch is shown in FIG. 1. The switch is provided with movable contact carriers 102, each of which holds an electrically conductive contact 104. The contact carriers 102 are mounted on a bail 106, which is pivotally mounted in the switch housing 108. Pairs of stationary electrical contacts 110, 112 are also mounted within the switch housing 108 so as to receive the movable contacts 104 when the switch is "ON". One electrical contact 110 in each pair is connected to a line voltage while the other electrical contact 112 in each pair is connected to a load.
A handle 114 is connected to the bail 106 by way of a loading/actuating mechanism 115. In the switch of FIG. 1, the loading/actuating mechanism comprises a drive shaft 116 (coupled to the handle 114) and an operating cam 118. A spring 120 is mounted to the switch housing 108 and coupled to the bail 106 so as to bias the bail 106 in a position such that each of the movable contacts 104 will be brought into mechanical and electrical connection with a corresponding pair of the stationary contacts 110, 112. A rod 122, centered within the spring transfers the force of the spring to the cam 118. By pulling the handle 114 down, the user loads the spring 120 which, in turn, pivots the bail 106 into an "over center" position away from the stationary contacts, thus leaving the switch in an "OFF" or "open" position.
When the handle 114 is moved in an upward direction by the user, the cam 118 pivots the bail 106. Once pivoted beyond the center position, in the direction of the stationary contacts 110, 112, the bail 106 slips from the handle 114 as the spring 108 pushes the bail 106 into place. When the bail is in place in it's spring biased position, the movable contacts 104 each make mechanical and electrical connection between a corresponding pair of stationary contacts 110, 112, thus placing the switch into a "ON" or "closed" position.
An auxiliary switch 124 may be mounted in a position within the housing such that the heel of the bail 106 will cause the auxiliary switch 124 to be "closed" just after the bail 106 and contacts 104 are pushed into a "closed" position by the spring 120. The auxiliary switch 124 is typically used to provide a positive indication of the condition (OPEN or CLOSED) of the safety switch.
A more detailed view of the loading/actuating mechanism 115 of FIG. 1 is shown in FIG. 2. The cam 118 includes a tab having a notch 118a. The coil portion of a torsion spring 202 is positioned over the drive shaft 116. The formed leg 202a of the torsion spring 202 is hooked under the adjacent leg of the bail 106. The straight leg 202b of the torsion spring 202 is inserted into the notch 118a provided for that purpose in the cam 118.
The bail 106 is placed between an upper stop 118b and a lower stop 118c of the cam 118. The torsion spring 202 exerts a force on the bail 106 holding it against the upper stop 118b on the cam 118. This prevents the movable contacts 104 from be placed, by gravity or mechanical shock, into inadvertent engagement with the stationary contacts 110, 112. A handle biasing spring (not shown) can also be provided so as to ensure that the position of the handle 114 is indicative of the position of the cam 118.
In many applications, it would be advantageous to be able to turn off the safety switch from a remote location. Remote opening is known, for example, in circuit breakers and molded case switches. Thus, while the remote control of switches is known in the art, what is needed is a mechanism that is specifically suited for the structure of spring operated safety switches.